1. Field of the Invention
The present invention pertains to apparatus for scraping the outer cooling surfaces of freezer drums, and in particular to the scraping of freezer drums to remove frost and ice formations thereon.
2. Description of the Related Art
Rotating drums having outer refrigerated surfaces are used for continuous cooling or freezing of products brought in contact with the refrigerated surface. For example, U.S. Pat. No. 4,349,575 describes a "blanket" of meat material in paste form applied to the outer surface of a rotating drum. The drum is refrigerated so as to freeze the paste material, which is removed from the drum surface as a flat, continuous sheet. The drum freezer is operated at temperatures which cause ambient moisture in the operating environment to accumulate on the drum surface as frost or ice. A stationary scraper blade scrapes across the drum surface to remove accumulated moisture which has been transformed into a solid. An evacuated hood surrounds the scraper blade and removes the scraped material from the operating environment.
U.S. Pat. No. 4,332,143 to Soecknick, et al. discloses a movable ice scraper disposed at the intake of a gas cooling device. The heat transfer portion of the device and the ice scraper have telescopic, tubular forms, with the tubular ice scraper traveling within the heat transfer tube. An external piston, having a central axis generally parallel to the axis of the ice scraper tube, is connected thereto, to reciprocate the ice scraper within the heat transfer tube. The ice scraper tube is operated periodically to remove ice which has formed in the bore of a heat transfer tube.
U.S. Pat. No. 4,662,183 also discloses a tubular heat exchanger with an internal piston scraping the tube bore to remove ice formed thereon, harvesting the ice for subsequent consumption. U.S. Pat. No. 2,549,215 also discloses an arrangement for harvesting ice, and employs a trip hammer which beats against a freezer drum surface to break ice accumulated thereon. The broken ice is collected for subsequent consumption.
Swept surface or scraped surface heat exchangers are also known in the art. For example, U.S. Pat. No. 2,930,058 discloses a tubular freezing chamber having a central axis. Scraper blades mounted for rotation about the axis scrape the tube bore to remove frozen materials formed thereon. U.S. Pat. No. 2,867,987 also discloses a rotating scraper in the bore of a freezing apparatus.
U.S. Pat. No. 1,966,099 discloses a defroster for removing accumulations from the refrigerator coils of ice making machines. A lever mounted on a rotating wheel is disposed above the refrigerator coil. When frost and ice accumulated on the refrigerator coil are built up to a preselected thickness, the lever is tripped, initiating a heated defrost cycle.
Other arrangements for detecting frost and ice buildup on a refrigerator surface, for initiating a defrost cycle, may take other forms. For example, U.S. Pat. Nos. 4,348,869 and 4,428,206 employ ultrasonic transducers to monitor frost and ice accumulation, either directly by using echo-ranging techniques, or indirectly, by measuring deflection of a mechanical probe.
As can be seen from the above, and as will be appreciated by those skilled in the art, commercial production facilities using freezer drums in production operations typically require some means for controlling the accumulation of frost and ice on the freezer surfaces in order to maintain efficient heat transfer rates. Despite advances provided by the above, a need still exists for an improved frost and ice removal system which is suitable for either automatic or semiautomatic operation.